The invention relates to a method for predetermining a motion state of a driveshaft of an internal combustion engine. Said method, which is performed by means of a controller for start-stop operation of an internal combustion engine in a motor vehicle, serves to realize the so-called engagement upon run-down. Engagement upon run-down means that a starting pinion of a starting device, preferably in the form of a preengaged drive starter, engages into a still-rotating toothed ring of the internal combustion engine. A still-rotating toothed ring of the internal combustion means that the standstill state, that is to say the discontinuance of rotation of the driveshaft of the internal combustion engine, is already planned, intended or has already been initiated. During said run-down, the rotational speed of the driveshaft decreases macroscopically. Considering the run-down of the driveshaft of the internal combustion engine in detail, however, it can be seen that said macroscopic run-down is characterized by relative minima and maxima and accordingly rotational speed increases and rotational speed decreases. Said rotational speed fluctuations during the macroscopic run-down have the result that the starting pinion can seldom, or not at all, be engaged into the toothed ring in such a manner as to protect the transmission. The problem here is the adaptation of the circumferential speeds, that is to say substantially the alignment of the circumferential speeds of toothed ring and starting pinion, which is difficult. Differences in the circumferential speeds have the result that the teeth of the starting pinion and toothed ring are subjected to alternating impact loading. Furthermore, an early starting of the starting pinion with high load can have the result that the starting pinion on the one hand cannot at all engage into the toothed ring, instead to some extent “ratcheting” with its teeth against the teeth of the toothed ring, and as a result the starting pinion and its teeth are subjected to considerable wear. If the starting pinion has however already been engaged slightly into the toothed ring but is already under high torque loading, there is the risk, owing to a possibly only slight degree of overlap of teeth on the toothed ring and teeth on the starting pinion, that the teeth are generally loaded only over a short distance, instead being loaded at said point with a uniform load or tooth load which is too high for said short degree of overlap. There is the risk here of teeth, or parts of said teeth, breaking away. To nevertheless permit engagement upon run-down only with low loading for the starting pinion and toothed ring, the most precise possible preparation for said mutual engagement is necessary. Within the context of said preparation, it is provided that a suitable engagement time be predicted.
Already known from the prior art are various proposals for engagement into the toothed ring during the run-down of the internal combustion engine and thus shortening of the starting time.
DE 10 2006 011 644 A1 discloses a device and a method for operating a device having a starter pinion and having a toothed ring of an internal combustion engine, wherein the rotational speed of the toothed ring and of the starter pinion are determined in order, after the shut-down of the internal combustion engine, to engage the starter pinion at substantially identical rotational speed during the run-down of the internal combustion engine. Values from a characteristic map of a control unit are assigned for determining the synchronous engagement rotational speeds.
DE 10 2006 039 112 A1 describes a method for determining the rotational speed of the starter for a motor vehicle internal combustion engine. It is also described that the starter comprises its own starter control unit for calculating the rotational speed of the starter and, during start-stop operation, accelerating the pinion of the starter initially without engagement when self-starting of the internal combustion engine is no longer possible as a result of the rotational speed having dropped. The pinion is meshed at a synchronous rotational speed into the toothed ring of the running-down internal combustion engine.
DE 10 2005 004 326 describes a starting device for an internal combustion engine with a separate engagement and starting process. For this purpose, the starting device has a control unit which activates separately a starter motor and an actuating element for engaging a starter pinion. By means of the control unit, the pinion can be engaged into the toothed ring before a starting process of the vehicle before the driver has expressed a new starting demand. Here, the actuating element, in the form of an engagement relay, is activated already during a run-down phase of the internal combustion engine. Here, the rotational speed threshold lies far below the idle rotational speed of the engine in order to keep the wear of the engagement device as low as possible. To prevent voltage drops in the on-board electrical system as a result of a very high starting current of the starter motor, a smooth start is realized by means of the controller for example through pulsing of the starter current. The power capacity of the on-board electrical system is monitored by analysis of the battery state, and the starter motor is pulsed or supplied with current correspondingly. The invention also describes that the crankshaft can be positioned shortly before or after the internal combustion engine comes to a standstill, in order to shorten the starting time.
DE 10 2005 021 227 A1 describes a starting device for an internal combustion engine in motor vehicles, having a control unit, a starter relay, a starter pinion and a starter motor for a start-stop operating strategy.
By contrast to the already known methods, it is the intention to provide a method by means of which a restart of the internal combustion engine can be carried out not only more quickly but rather also with increased precision and thus reduced wear of the starter pinion and toothed ring.